Ah, the eternal hills! Or are the hills eternal? Not according to what we know of our geology. The Restless Earth might be a more meaningful description. Over times unimaginably long to short-lived humans, the land has risen and fallen, the sea encroached and retreated, and the very continents wandered the face of the earth.
Many an El Pasoan can look out their house or car windows and see
abundant evidences of the earth's fitful activity. Among these are the Franklin and
Juárez mountains and the Rio Grande Valley. The Franklin Mountains more or less rose in
place, tilting as the land pulled apart, but the Juárez Mountains are an entirely
different story. Some 50 million years ago, huge sheets of limestone were slowly pushed
to the northeast by massive compressive forces and, overriding one another, piled up to
form today's mountain mass. Later, about 35 million years ago, the earth's
crust began to pull apart, forming what today we call the Rio Grande Rift after the
river that follows its pathway from Colorado to Mexico.
Contributor: Arthur H. Harris, Laboratory for Environmental Biology, Centennial Museum, University of Texas at El Paso.
Desert Diary is a joint production of the Centennial Museum and KTEP National Public Radio at the University of Texas at El Paso.
The Franklin Mountains, looking east from west of the Rio Grande Valley. Photograph by A.H. Harris.
Lovejoy, E. M. P. 1972. The Stratigraphy and Structure of the Sierra de Juarez, Chihuahua, Mexico. El Paso Geological Society Publication, 56 pp.
A Brief Geological History of the EL PASO-JUAREZ (ELP-J) Region